Generally, an integrated circuit (“IC”) is a circuit in which all or some of the circuit elements are inseparably associated and electrically interconnected so that it is considered to be indivisible. An IC is commonly embodied in a wafer. A wafer can be a slice or flat disk of semiconductor material or, for example, of semiconductor material deposited on a substrate, in which circuits or devices are simultaneously processed and, if there is more than one device, subsequently separated into dies. The wafer can have logic circuitry that forms a high-speed digital circuit, such as digital logic for a digital phase locked loop (“PLL”) circuit, for example.
A ring oscillator is a component of the PLL circuit that facilitates clock generation in a wide range of application-specific integrated circuits (ASICs) including, but not limited to, network controllers, I/O controllers, graphics processors, or the like. As such, the DCO covers a wide frequency range for process, voltage, and temperature (PVT) variations, and also has a fine resolution. However, there is a need to improve the ring oscillator and the phase noise of the PLL.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.